1. Field of the Invention
The present invention relates to subsea pipelines and connectors and/or fittings used in the pipelines. In particular, the invention relates to a subsea fitting that clamps around a portion of a subsea pipeline and provides internal pressure-sealed regions inside the fitting.
2. Description of Related Art
Subsea pipelines are used to transport oil and gas to shore from offshore platforms and other pipeline systems. During use of the pipeline, the pipeline flow in a specific line may need to be interrupted or “plugged” internally to prevent loss of product to the subsea environment during maintenance and/or repair operations on the pipeline. Typically, a mechanical bolt-on split sleeve hot tap fitting and tapping valve are placed on the pipeline. A “hot tap” machine is then used to cut a hole in the pipeline within the pressure-containing confines of the mechanical bolt-on split-sleeve hot tap fitting and tapping valve. After the tap is completed, a plugging machine is mounted to the tapping valve and used to install a temporary plugging head into the pipeline. The plugging head blocks the flow of the product in the pipeline to allow the pipeline operator to cut or otherwise modify the pipeline downstream from the plugging head without emission of any pipeline product. However, before cutting the pipeline, all remaining product in the isolated downstream section of the line is drained through a separate hot tap fitting (typically, a 2″ hot tap fitting). The separate hot tap fitting is typically of the same design as the plugging hot tap fitting.
After the completion of the required maintenance and/or repair operations, the operator restores flow in the pipeline by retracting the head of the plugging machine from the interior of the pipeline. However, because of the design of the plugging head, the plugging head cannot be removed against a differential pressure. Therefore, pressure is introduced through the separate hot tap fitting (the 2″ hot tap fitting) to equalize pressure on both sides of the plugging head to permit retraction of the plugging head. Thus, the separate hot tap fitting is used for both draining excess product and equalizing pressure prior to removal of the plugging head.
Currently, the separate hot tap fitting is a totally separate fitting from the plugging hot tap fitting. Thus, two separate installations are required to install the separate hot tap fitting and plugging hot tap fitting. To avoid using multiple fittings and to reduce installation costs, a unique subsea fitting is proposed that integrates the separate hot tap fitting and the plugging hot tap fitting into a single fitting. The elimination of the separate hot tap fitting may reduce the costs (e.g., costs associated with equipment, surface vessels, manned diving operations, and the like) and significantly reduce the time required to install multiple fittings subsea.
Currently, separate fittings are used to provide bypass and plugging functions on a subsea pipeline. One fitting may be used to allow insertion of the plugging head into the pipeline while another fitting upstream of the plugging head is used to divert fluid flow into a bypass line. Proposed is a unique subsea fitting that may be able to provide both the bypass and plugging functions in a single fitting. The single fitting eliminates separate fittings for connection to the bypass line and insertion of the plugging head.
Clamp fittings are typically used to seal off a portion of a subsea pipeline, for example, when the pipeline begins to leak in a certain location. Installation of the clamp fittings can be time consuming and costly. Proposed is a simplified clamp fitting that reduces the number of steps needed to install the clamp fitting and may reduce equipment costs and installation costs associated with installing the clamp fitting.